Study On Enzyme Treatment Before And After Oxygen Delignification Of Acacia Kraft Pulp

The effects of enzyme treatments on oxygen delignification of Acacia kraft pulp and its mechanism were investigated. It was explored the influences of the enzyme treatments on delignification rate and degradation of carbohydrate during the oxygen delignification process. The results are of great significance to improve the oxygen delignification and enzyme industrial application.The enzyme treatment before and after oxygen delignification were studied. It was researched the influences of enzyme pretreatment on the three primary variables in the subsequent oxygen delignification process. The effects of enzyme treatments on oxygen delignification between high-lignin content pulp and low-lignin content pulp, pretreatment and sebsuquent treatment, and four types of enzyme systems were compared. The mechanism was also investigated by analysis of the hexenuronic acid content in the pulp, SEM observation of the fibers'microstructure, and determination of the sugar content in the filtrate by HPLC. The results indicated:1,The optimum enzyme dosage of LXS in the pretreatment of low-lignin content pulp was 7IU/g, in the subsequent process it was 5IU/g and treated for 2 hours. The three primary variables of oxygen delignification after LXS pretreatment were: alkali dosage 2.5%, treated for 60 min at 100℃.2,The optimum conditions of X in the pretreatment of low-lignin content pulp were: X dosage 4 IU·g^-1, treated for 1.5 hours; in the subsequent process they were: X dosage 4 IU·g^-1,treated for 1 hour. The optimal alkali dosage was 2.5% in the subsequent oxygen delignification process.3,The results of subsequent treatment of both LXS and X were better than that of the pretreatment. Compared with X, LXS was better in improving the delignification rate and pulp strength. X was more effective in improving the whiteness of pulp.4,The optimum enzyme dosage of LXS in the pretreatment and subsequent of high-lignin content pulp were 7IU/g and 5IU/g respectively; for X, they were 6 IU/g and 4 IU/g respectively.5,The effects of enzyme treatment on oxygen delignification were more significant in high-lignin content pulp than in low-lignin content pulp. After subsequent treatment of LXS, the delignification rate of oxygen increased by 11 percents; the viscosity was not dropped obviously; the whiteness of pulp increased by 4% ISO. After subsequent treatment of X, the whiteness of pulp can be increased by 7% ISO.6,XHT was the most appropriate enzyme to combine with oxygen delignification in the four enzyme systems to improve the delignification effects and drop the application costs.7,The effects of enzyme treatments obviously decreased after Hex.A was removed from the pulp. SEM observation of the microstructure indicated that the fiber surface was rough and there were many tiny holes and cracks in the cross section of the cell wall after the enzyme treatment, among which the subsequent treatment pulp was most obvious.8,HPLC analysis of the filtrate before and after oxygen delignification showed that the xylose content was relatively high in the X subsequent filtrate. It indicated that X had better effects on degradation of xylan.